[spec] Specific hypermedia link to the stop database

[pietercolpaert]

Optionally, all data necessary (to be defined what this means in #10) of the stops can be included in the page of the connections.

If however an external resource is available for more data on the stations, we should make sure this resource is linked from this page.

Requirements:

• Link to a specific page (or a tree:Node) that can give a part of the stops, but contains links to the full collection too
• Link to 1 file that contains all stops should work too